What should you do if an ant crawls in your ear?

Ant Stings. I agree w dr ferguson. If this is a fire ant it is important to take action as fire ants can repeatedly sting you. They inject solenopsin - an alkaloid venom. About 15% of people who have been stung are allergic. In some cases this causes anaphylaxis. For a significant allergic reaction to fire ant stings call 911 or be evaluated at the nearest emergency room.
Suffocate the bug. If this did happen, I would get some baby oil, fill up the canal & plug it with cotton & ignore it for a while. You can replace the oil several times over a day or two, then flush out the dead bug with a simple ear was product (murine makes a handy canister).